 (function (doc, win) {  
          var docEl = doc.documentElement,  
            resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',  
            recalc = function () {  
              var clientWidth = docEl.clientWidth;  
              if (!clientWidth) return;  
              docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';  
            };  
  
          if (!doc.addEventListener) return;  
          win.addEventListener(resizeEvt, recalc, false);  
          doc.addEventListener('DOMContentLoaded', recalc, false);  
        })(document, window);  